Circuit emulation service over an internet protocol network

ABSTRACT

The present invention establishes a circuit emulation service (CES) over an internet protocol (IP) network based on properties of the IP network. The CES emulates a circuit from a local interworking function to a remote interworking function. Data that is received at a constant bit rate at the local interworking function is encapsulated into a number of IP packets configured according to the CES. The IP packets are transported from the local interworking function to the remote interworking function according to the CES. In one embodiment, each IP packet also includes data segments for simultaneously encapsulating multiple constant bit rate circuits. In another embodiment, each data segment includes a separate CES circuit header.

FIELD OF THE INVENTION

[0001] The present invention pertains to the field of networking. Moreparticularly, this invention relates to circuit emulation services overan internet protocol (IP) network.

BACKGROUND OF THE INVENTION

[0002] Over the years, a wide variety of networks have been developed tocarry various types of information. Early networks were telephonenetworks designed with voice communications in mind. These networkswere, and still are, primarily circuit-based networks. In acircuit-based network, each call establishes a dedicated, point-to-pointconnection through the network which, for instance, allows people atboth ends of a telephone call to speak and listen at the same time.

[0003] A circuit remains open for the entire duration of a call even ifno one is speaking. In which case, a large portion of circuit'sbandwidth, or capacity to carry information, is wasted on silence, ormeaningless data. Time Division Multiplexing (TDM) is a commoncircuit-based technology. In TDM, analog signals are digitally coded andmultiplexed in time over circuits at a constant bit rate.

[0004] In recent decades, the wide spread use of computers has led tothe development of additional types of networks. These networks havebeen designed with data communications in mind and are primarilypacket-based networks. In a packet-based network, a call may consist ofa stream of data sent from one computer to another. The stream of datais divided up into packets before it enters the network. At thedestination, the stream of data is re-assembled from the packets.

[0005] A packet-based call does not require a dedicated connectionthrough the network. Instead, packets from many different calls canshare the same bandwidth. That is, packets from one call can be insertedinto spaces between packets from other calls. In which case,packet-based networks efficiently utilize much more network bandwidththan circuit-based networks, making packet-based networks particularlysuited to handle the large volumes of data traffic.

[0006] Packet-based networks, however, normally do not work well fortime critical transmissions such as voice. For instance, in packet-basednetworks, packets may experience delay variations while travelingthrough the network. As a result, packets are rarely received at aconstant bit rate. In data communications, delay variations betweenpackets usually do not matter. A computer can just wait for a completeset of packets to arrive before processing the data. For time criticaltransmissions however, delay variations can have a significant impact onthe quality of the call. In which case, circuit-based networks like TDMare generally better suited for constant bit rate, time criticaltransmissions such as voice.

[0007] Since packet-based and circuit-based networks are suited todifferent kinds of data, network carriers often have to maintain morethan one kind of network to satisfy client needs. A carrier may need tomaintain TDM for voice and/or video, as well as packet-based networkssuch as frame relay, ATM (asynchronous transfer mode), and IP (internetprotocol) for data. In order to reduce the number of networks that mustbe supported, a network solution is needed that can provide theadvantages of both a circuit-based, constant bit rate service and apacket-based, high bandwidth utilization service.

[0008] One approach offered by an industry cooperation group, The ATMForum, is CES (circuit emulation service) over ATM. CES over ATM isdescribed in “Circuit Emulation Service Interoperability Specification,”AF-SAA-0032.000, published September 1995, and “Circuit EmulationService Interoperability Specification Version 2.0,” AF-VTOA-0078.000,published January 1997, both available from The ATM Forum athttp://www.atmforum.com. CES over ATM establishes a logical path throughthe ATM network. In this respect, CES over ATM is similar to TDM in thatall the data in a circuit follows the same point-to-point path. With acommon path, there should be no out-of-order packets.

[0009] An ATM path can accommodate multiple circuits. Depending on adata rate needed for a given circuit, different amounts of bandwidth canbe assigned to different circuits in a path. As a result, delayvariations between packets should be greatly reduced.

[0010] Theoretically, CES over ATM eliminates the need for multiplenetworks because it allows ATM to handle regular data as well asconstant bit rate data. ATM, however, has a number of disadvantages andlimitations. For instance, ATM is not as widely spread as some othernetworks. The smaller ATM market share has lead to less research anddevelopment directed to future improvements, gaps in ATM availability,especially between regions serviced by different network carriers, andmore expensive ATM hardware and technical support. Other limitationsinclude security, in that ATM packet headers cannot be encrypted, andfailure recovery, in that data is often lost and re-routing is slowcompared to some other networks. For these and numerous additionalreasons, CES over ATM is less than an ideal network solution forconstant bit rate data transmission.

SUMMARY OF THE INVENTION

[0011] The present invention establishes a circuit emulation service(CES) over an internet protocol (IP) network based on properties of theIP network. The CES emulates a circuit from a local interworkingfunction to a remote interworking function. Data that is received at aconstant bit rate at the local interworking function is encapsulatedinto a number of IP packets configured according to the CES. The IPpackets are transported from the local interworking function to theremote interworking function according to the CES. In one embodiment,each IP packet also includes data segments for simultaneouslyencapsulating multiple constant bit rate circuits. In anotherembodiment, each data segment includes a separate CES circuit header.

[0012] Other features and advantages of the present invention will beapparent to those skilled in the art from the accompanying drawings andthe detailed description that follows below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Examples of the present invention are illustrated in theaccompanying drawings. The accompanying drawings, however, do not limitthe scope of the present invention. Similar references in the drawingsindicate similar elements.

[0014]FIG. 1 illustrates one embodiment of a circuit emulation serviceover internet protocol (CESIP).

[0015]FIG. 2 demonstrates one embodiment of CESIP from a sendinginterworking function.

[0016]FIG. 3 illustrates one embodiment of a CESIP packet.

[0017]FIG. 4 illustrates one embodiment of a CESIP circuit header.

[0018]FIG. 5 demonstrates one embodiment of CESIP from a receivinginterworking function.

[0019]FIG. 6 illustrates one embodiment of a re-assembly buffer.

[0020]FIG. 7 illustrates one embodiment of a hardware system

[0021]FIG. 8 illustrates one embodiment of a machine readable storagemedium.

DETAILED DESCRIPTION

[0022]FIG. 1 illustrates one embodiment of a circuit emulation serviceover an internet protocol (CESIP) network according to the teachings ofthe present invention. As discussed more fully below, CESIP leverages onthe many advantages of IP to provide a packet-based network solution forconstant bit rate data transmission such as voice and video. Like CESover ATM, CESIP is intended to emulate the circuit-based characteristicsof, for example, time division multiplexing (TDM) traffic.

[0023] In the illustrated embodiment, constant bit rate (CBR) circuits110 and 150, interworking functions (IWFs) 120 and 140, and IP network130 are coupled as shown. CBRs 110 and 150 represent any of a number ofdata sources having any of a number of signaling rates. For instance,CBR circuits 110 and 150 may represent any type of data traffic, such asvideo, digitized voice, frame relay, etc., between individual users,local area networks, internet service providers, or virtually any otherentity or combination of entities.

[0024] Those skilled in the art will be familiar with various signalingrates, such as structured and unstructured digital signal levels DS1,DS3, and NxDS0, and the European equivalents E1 and E3. For instance, aDS1 circuit can support 24 simultaneous 64 Kbps signals, a DS3 circuitcan support 28 DS1s, and an NxDSO can support N channels of 64 Kbpseach. CBR circuits 110 and 150 may also represent logical digital signalequivalent interfaces, such as interfaces that convert synchronoustransport signals (STS1) into DS3 or virtual tributary (VT1.5) into DS1.

[0025] As an overview, IWF 120 and IWF 140 exchange data to establishthe CESIP in IP network 130. In various embodiments, a request toestablish the CESIP can come through a CBR circuit itself, over asignaling channel, through a management system, etc. Once the CESIP isestablished, CBR circuit 110 begins providing a data stream to IWF 120at a constant bit rate. IWF 120 encapsulates the data into IP packets,attaches a predetermined CESIP header to each such IP packet, and feedsthe packets into IP network 130 through IP interface 125. The packetstravel through tunnel session 165 within tunnel 160 to IP interface 135.From IP interface 135, the packets arrive at IWF 140. IWF 140reassembles the data stream from the packets and provides the datastream to CBR 150 at the constant bit rate.

[0026] Those skilled in the art will recognize that, at various placeswithin an IP network, IP packets are often fragmented into smallerframes and eventually reassembled, wherein a payload for each framecomprises a portion of the original IP packet. As used herein, an IPpacket refers to a complete packet which may be fragmented into severalframes as it travels through an IP network. In which case, in theillustrated embodiment, a CESIP header is attached to a complete IPpacket, and not to individual fragments of the IP packet.

[0027] CESIP is preferable to CES over ATM for a variety of reasons. Forinstance, IP is more widely available than ATM. The cost associated withIP hardware and service is also lower than for ATM. IP has a higherdegree of interoperability than ATM in that IP can work with a widervariety of physical networks than ATM. IP's high degree ofinteroperability and wide availability also improve CES provisioning.For instance, providing an ATM connection from Boston, Mass. to SanJose, Calif. can take days. CES over ATM requires a permanent virtualcircuit that affects the actual operational aspects of the ATM network.Numerous physical connections have to be made and verified. IP, incontrast, is homogeneous so CESIP is available almost anywhere. Anywherethat internet access is available, CESIP is available.

[0028] Also, IP provides certain features, such as compression, headerencryption, and instantaneous failure recovery, that are not readilyavailable in ATM. ATM uses fixed length cells. There is no support forcompression in ATM. If useless data, such as silence, is received in aconstant rate bit stream, CES over ATM will transmit the useless data.IP, in contrast uses variable length packets. Numerous forms ofcompression are possible in CESIP to better utilize bandwidth byrecognizing useless data and not transmitting it.

[0029] Encryption is also more thorough in IP. In ATM, a headerdestination cannot be encrypted. With access to destination information,CES over ATM can be disrupted in numerous ways, such as flooding thedestination with data until the destination fails. In IP, a destinationheader can be encrypted while exposed on a public network, and onlydecrypted while in a trusted network.

[0030] ATM is connection oriented, so a failure requires reconstructionof a connection, or rerouting, around the failure. ATM re-routing cantake a comparatively long time and even cause data loss. IP, incontrast, is connectionless. For any given path, there is virtuallyalways an alternative path. IP does not rely on a particular route. If aroute fails, an alternative route is automatically used. Data is notlost. Instead there may merely be a temporary degradation in servicedue, for instance, to a longer alternate path through the IP network.

[0031] The fixed cell size of ATM makes ATM more easy to process througha network than the variable sized packets of IP. But, IP hardware hasadvanced faster than ATM hardware, allowing CESIP to sustain signalrates at least as fast as CES over ATM.

[0032] The present invention overcomes a number of obstacles inherent inIP so that the many advantages of IP can be utilized for circuitemulation services. For instance, compared to ATM, ATM preserves packetorder and defines a cell loss ratio through the ATM network. In whichcase, CES over ATM is relatively straight forward. IP packets, however,are often delivered out-of-order. In fact, IP provides no guarantee ofpacket delivery whatsoever. In which case, as discussed below, thepresent invention accounts for these and other properties inherent in IPto provide CESIP.

[0033]FIG. 2 demonstrates one embodiment of CESIP in more detail. Inblock 210, an interworking function (IWF) receives a request toestablish a CESIP. For instance, from a user's perspective, this couldbe dialing a phone number, submitting a login name, or clicking on alink to a web page. The request can come in any of a number of formats.In one embodiment, the request is received in a user command. In analternate embodiment, the request is received in an IP frame format. Inyet another embodiment, the request is received in a network managementprotocol such as simple network management protocol (SNMP). In eachcase, the request may include all or a portion of the controlinformation necessary to establish a CESIP. For instance, a CESIP mayalready be in place. In which case, the request may just include enoughinformation to identify the remote IWF so that the local IWF can verifythat the remote IWF exists on the IP network, and check on theavailability of an already configured CESIP.

[0034] If a CESIP has not already been established, and the remote IWFexists, the IWFs exchange control protocol information in block 220 toestablish a new CESIP. In one embodiment, CESIP builds upon an existingtunneling protocol, layer two tunneling protocol (L2TP). A tunneltransports packets across an intervening network in a way that isintended to be transparent to the end users. L2TP is described in detailin an Internet-Draft titled “Layer Two Tunneling Protocol ‘L2TP,’”published June 1999, and available from The Internet Society.

[0035] Basically, L2TP is an encapsulation protocol. Data isencapsulated before entering a network and then re-assembled whenleaving the network. A tunnel may include several tunneling sessions.That is, L2TP can keep track of several different bit streams between apair of two IWFs at the same time. Each CESIP uses its own L2TPtunneling session. In alternate embodiments, any number of tunnelingprotocols can be used.

[0036] The control protocol for CES layers on top of the tunnel andtunnel session of L2TP. In one embodiment, the CES control protocolinformation includes an alarm option, a compression option, an idlepattern option, a check sum option, and a clocking option, a packet sizeoption, a multiple circuit option, a maximum transmit delay, a maximumdelay variation, and an encryption option. The CES control protocol ismore easily understood in conjunction with the CESIP packet as discussedbelow.

[0037] Once a CESIP has been established, data is received at a constantbit rate in block 230. In block 240, the data is encapsulated into IPpackets with additional headers. And, in block 250, the packets are sentthrough the IP network.

[0038]FIG. 3 illustrates one embodiment of an encapsulated CESIP packet300. In the illustrated embodiment, CESIP packet 300 includes a numberof known, standard headers including medium dependent header 305, IPheader 310, UDP header 315, and L2TP header 320. Medium dependent header305 depends on the underlying network. For instance, the header may bedifferent if the physical medium is a synchronous optical network(SONET), a copper line, a coaxial cable, or a digital wirelesstransmission. The header may actually include more than one header suchas an ATM header and a SONET line header. The header will change as thepacket moves through different types of networks. For instance, eachrouter may internetwork two different kinds of networks. So, at eachrouter, the packet may get repackaged with a different medium dependentheader 305.

[0039] IP header 310 includes a length indicator for the variable lengthIP packet. During configuration, the CES control protocol establishes amaximum and minimum packet length. The length may depend on how reliablethe network is believed to be. That is, the physical network medium hasassociated with it a bit error rate, such as one bit error per Xmegabits. A longer packet has a higher probability of experiencing a biterror. Once a packet is corrupted by a bit error, the packet will likelybe dropped. In which case, a more reliable network can support a longerpacket size and still maintain a low probability of experiencing a biterror.

[0040] Following IP header 310 is user datagram protocol (LJDP) header315. If L2TP can work directly with IP packets, then UDP header 315 isoptional.

[0041] Following the standard headers, the illustrated embodimentincludes optional security header 325. If it is used, security header325 may include customized security information, for instance, forauthentication and encryption. Alternately, a standardized securityheader can be used such as the IP security header, IPSec, which includesa separate authentication header section and an encryption headersection. If an IPSec header is used, it is usually located between IPheader 310 and UDP header 315 in the IP packet rather than followingL2TP header 320.

[0042] Following security header 325, the illustrated embodimentincludes CESIP header 330. In one embodiment, CESIP header 330 containsonly a version number for compatibility purposes between hardware ateach IWF. Additional information pertaining to individual CESIP circuitsis stored in the respective circuit entries as discussed below.

[0043] The illustrated embodiment contains N circuit entries. That is,if the multiple circuit option was enabled during the CES controlprotocol configuration, each packet can contain data from multipledifferent circuits. For instance, referring to FIG. 1, if fivesimultaneous data streams are being sent from CBR 110 to CBR 150 atconstant bit rates, data from all five data streams can be encapsulatedin one CESIP packet. Each circuit entry includes a circuit headersection, such as headers 335 and 345, and a circuit data section, suchas sections 340 and 350.

[0044] Enabling multiple circuits per packet can reduce overhead. Forinstance, less bits are needed for header information if multiplecircuits are included in one packet. Also, less packets need to berouted through the network if multiple circuits are included in onepacket. The drawback to packets containing multiple circuits isincreased packet length. As discussed above, longer packets have ahigher probability of a bit error. In which case, the option to includemultiple circuits per packet, as well as the number of circuits perpacket, may depend on the estimated reliability of the underlyingphysical network.

[0045] Following the circuit section of CESIP packet 300, theillustrated embodiment includes an optional check sum field 355. Duringconfiguration, the CES control protocol determines whether packets willinclude a check sum. If both users agree that the underlying network isexceptionally reliable, the check sum can be disabled to save somebandwidth. Any number of check sum formats could be used to identifyvarious errors in CESIP packet 300.

[0046]FIG. 4 illustrates one embodiment a circuit header 335 from FIG. 3in more detail. Circuit header 335 includes circuit identification 405to identify which circuit is being emulated. Circuit header 335 alsoincludes flags field 410. One embodiment of flags field 410 includes acompression flag, idle flag, alarm indication signal (AIS) flag, andclocking information. All four of these flags are setup during the CEScontrol protocol configuration. If the compression option is enabledduring configuration, then the compression flag for a particular circuitin a packet is set when the circuit data has been compressed. Even ifcompression is enabled though, not all data is compressible. In whichcase, the compression flag is only set if data needs to be decompressedat the receiving end. If the compression option is disabled, no attemptis made to compress data and the compression flag is never set.

[0047] During configuration, the idle condition option determines howidle conditions are to be treated. An idle condition is usually apredetermined bit pattern that indicates no useful data is being sent.If a sending IWF receives an idle pattern in the input data stream,there is no need to transmit the idle data. Rather, the idle flag can beset to indicate an idle state and the data field for the idle circuitcan be dropped off the packet. The frequency at which the packets aresent during idle can also be reduced. The reduced frequency can be setduring the control protocol configuration. For instance, during normalemulation of a DS3 circuit, an IWF may send packets at a rate of 8 KHz.During idle however, the IWF may send only one packet per second. Or, inthe case of a multiple circuit packet where only one circuit is idle,the idle circuit may be excluded from the packets being sent at 8 KHzand only included in one packet per second.

[0048] The alarm indication signal is similar to the idle flag. If analarm state is detected, such as an abrupt and unexpected stall in theconstant input bit stream at an IWF, an alarm pattern should be insertedinto the bit stream. Rather than sending the alarm pattern in the dataportion of the packet, the data portion can be dropped off and the alarmflag set. Then, the receiving IWF, which was configured by the CEScontrol protocol with the appropriate alarm pattern, can insert thealarm pattern from the receiving end based on the alarm flag. A greatdeal of network bandwidth can be saved by not sending the alarm patternover the CESIP. The alarm pattern may be different for different typesof signal rates, such as DS3 and the European equivalent. An alarm flagmay also reduce the transmission rate similar to the way an idle flagcan reduce the transmission rate.

[0049] In one embodiment, the clocking flags will only be included ifthe CES control protocol configuration indicates that the CESIP isasynchronous. The clocking flags are used for clock synchronizationbetween a pair of IWFs. Any number of clocking flag formats could beused. In one embodiment, a synchronous residual time stamp (SRTS) isused. Those skilled in the art will be familiar with clocksynchronization using SRTS in CES over ATM. In one embodiment, CESIPsupports SRTS in a fashion similar to CES over ATM in that CESIP uses afour bit SRTS with one bit in each alternate packet so that a completeSRTS value is obtained once every eight packets. Alternately, all of theclocking bits can be stored in one packet, or spread over more or fewerpackets. In a synchronous CESIP, the clocking flags are not neededbecause the IWFs are already synchronous.

[0050] Returning to FIG. 4, following flag field 410 is sequence number415. Sequence number 415 is used to reassemble the data stream from thepackets of data. In an IP network, packets may take different routes andbecome out-of-order. The sequence number is used to reassemble thepackets in data stream order. In one embodiment, sequence number 415 isan offset value for the packet of data in the stream of data withrespect to some reference point. Bits in the incoming bit stream arecounted with respect to a reference bit, such as the first bit in a datastream, as the bits are encapsulated. Each packet is given an offsetvalue equal to the bit number of the first bit in the packet withrespect to the reference bit. As discussed below with respect to FIG. 6,at the receiving IWF, the packets are buffered so that out of orderpackets can be assembled in order.

[0051] In one embodiment, the offset number is 32 bits. In which case,the offset number wraps around to zero after more than 4 Gbits of data.So, as long as an out-of-order packet does not arrive more than 4 Gbitslate, the receiving IWF will either be able to fit it in to the datastream or identify it as an old packet that should be dropped.

[0052] In FIG. 4, following sequence number 415 is first octet padding420 and last octet padding 430. These two values are used to maintainbyte alignment in the data encapsulated in the packet. For variousreasons, processing speed is increased if byte alignment is maintained.During encapsulation however, packets may not begin and end on byteboundaries, so bits are often added at the beginning and end of the dataportion of a circuit within a packet to maintain byte alignment.Therefore, to prevent the padded bits from being added to the outputdata stream, padding value 420 indicates how many bits in the first byteof the data portion of a circuit are not part of the data stream andpadding value 430 indicates how many bits at the end of the last byte ofthe data portion of the circuit are not part of the data stream so thatthe bits can be skipped.

[0053] Those skilled in the art will recognize that any number ofadditional approaches can be used to maintain byte alignment. Forinstance, if the data stream is encapsulated in a byte aligned manner,every bit in a data field will be fill by the data stream so that thepadding values 420 and 430 can be excluded from the circuit headerformat.

[0054]FIG. 5 illustrates one embodiment of a CESIP from the perspectiveof the receiving interworking function (IWF). In block 510, a request isreceived to establish a CESIP. For instance, this request can bereceived over the IP network as an IP packet. In block 520, the samecontrol protocol information is exchanged as discussed above. In block530, packets are received. As discussed above, the packets may includedata from multiple circuits. In block 540, the packets are assembled ina buffer based on the sequence numbers in each circuit header, and inblock 550 the buffered data is delivered at the constant bit rate.

[0055]FIG. 6 illustrates one embodiment of a buffer to reassemble acircuit. The packets cannot be buffered for an extended period of time.For instance, for voice communications, the constant bit rate data canonly be delayed for up to 30 to 50 milliseconds in order to maintain aTDM quality connection. Also, buffer 600 should be short enough so thatold packets can be identified using, for instance, the offset numbersdiscussed above. On the other hand, buffer 600 needs to store packetslong enough to account for maximum delay variations. For instance,during CES control protocol configuration, a maximum delay variation isagreed upon by the IWFs, and may be in the neighborhood of 10milliseconds.

[0056] Delay variation is dependent upon network traffic. If a largevolume of traffic is passing through the network, routers are likely tohave longer delays because packets have to sit in longer queues to beprocessed. Delay variation is also dependent upon the path that a packettakes through the IP network. Different paths usually have differentpropagation delays. Different propagation delays can cause packets toarrive out of order. By allowing packets to accumulate for at least aslong as the maximum delay variation, the chances of loosing packets dueto delay variation are greatly reduced.

[0057] In the illustrated embodiment, buffer 600 includes a low watermark 610 and a high water mark 620. Bit stream data are accumulateduntil low water mark 610 is reached before transmitting output stream630. If high water mark 620 is reached, buffer 600 has overflowed. Datamust be discarded if buffer 600 has overflowed. In one embodiment andentire buffer content is discarded. Alternately, data is discarded downto below low water mark 610. If data is lost, a predetermined bitsequence can be inserted. For instance, unstructured DS3 uses a framed1010 . . . alarm bit pattern. E3, the European equivalent, uses a 1111 .. . bit pattern.

[0058] In various embodiments, packet routing techniques can be used toincrease the likelihood that packets will follow the same path throughthe network and, therefore, reduce large delay variation andconsequently data loss due to late packet arrival. Those skilled in theart will be familiar with routing techniques such as source routing,RSVP (resource reservation protocol), MPLS (multi-protocol labelswitching), and provisioned flows using a packet filter.

[0059]FIG. 7 illustrates one embodiment of a hardware system intended torepresent a broad category of computer systems such as personalcomputers, workstations, and/or embedded systems. In the illustratedembodiment, the hardware system includes processor 710 coupled to highspeed bus 705, which is coupled to input/output (I/O) bus 715 throughbus bridge 730. Temporary memory 720 is coupled to bus 705. Permanentmemory 740 is coupled to bus 715. I/O device 750 is also coupled to bus715. I/O device(s) 750 may include a display device, a keyboard, one ormore external network interfaces, etc.

[0060] Certain embodiments may include additional components, may notrequire all of the above components, or may combine one or morecomponents. For instance, temporary memory 720 may be on-chip withprocessor 710. Alternately, permanent memory 740 may be eliminated andtemporary memory 720 may be replaced with an electrically erasableprogrammable read only memory (EEPROM), wherein software routines areexecuted in place from the EEPROM. Some implementations may employ asingle bus, to which all of the components are coupled, or one or moreadditional buses and bus bridges to which various components can becoupled. Those skilled in the art will be familiar with a variety ofalternate internal networks including, for instance, an internal networkbased on a high speed system bus with a memory controller hub and an I/Ocontroller hub. Additional components may include additional processors,a CD ROM drive, additional memories, and other peripheral componentsknown in the art.

[0061] In one embodiment, the circuit emulation service over internetprotocol (CESIP), as described above, is implemented using one or morecomputers such as the hardware system of FIG. 7. Where more than onecomputer is used, the systems can be coupled to communicate over anexternal network, such as a local area network (LAN), an IP network,etc. In one embodiment, the present invention is implemented as softwareroutines executed by the computer(s). For a given computer, the softwareroutines can be stored on a storage device, such as permanent memory740. Alternately, as shown in FIG. 8, the software routines can bemachine executable instructions 810 stored using any machine readablestorage medium 820, such as a diskette, CD-ROM, magnetic tape, digitalvideo or versatile disk (DVD), laser disk, ROM, Flash memory, etc. Theseries of instructions need not be stored locally, and could be receivedfrom a remote storage device, such as a server on a network, a CD ROMdevice, a floppy disk, etc., through, for instance, I/O device 750. Theinstructions may be copied from the storage device into temporary memory720 and then accessed and executed by processor 710. In oneimplementation, these software routines are written in the C programminglanguage. It is to be appreciated, however, that these routines may beimplemented in any of a wide variety of programming languages.

[0062] In alternate embodiments, the present invention is implemented indiscrete hardware or firmware. For example, one or more applicationspecific integrated circuits (ASICs) could be programmed with the abovedescribed functions of the CESIP. In another example, the CESIP could beimplemented in one or more ASICs on additional circuit boards and thecircuit boards could be inserted into the computer(s) described above.In another example, field programmable gate arrays (FPGAs) or staticprogrammable gate arrays (SPGA) could be used to implement the presentinvention. In yet another example, a combination or hardware andsoftware could be used to implement the present invention.

[0063] Thus, a circuit emulation service over internet protocol isdescribed. Numerous specific details have been set forth in order toprovide a thorough understanding of the present invention. However,those skilled in the art will understand that the present invention maybe practiced without these specific details, that the present inventionis not limited to the depicted embodiments, and that the presentinvention may be practiced in a variety of alternate embodiments. Inother instances, well known methods, procedures, components, andcircuits have not been described in detail.

[0064] Parts of the description have been presented using terminologycommonly employed by those skilled in the art to convey the substance oftheir work to others skilled in the art. Also, parts of the descriptionhave been presented in terms of operations performed through theexecution of programming instructions. As well understood by thoseskilled in the art, these operations often take the form of electrical,magnetic, or optical signals capable of being stored, transferred,combined, and otherwise manipulated through, for instance, electricalcomponents.

[0065] Various operations have been described as multiple discrete stepsperformed in turn in a manner that is helpful in understanding thepresent invention. However, the order of description should not beconstrued as to imply that these operations are necessarily performed inthe order they are presented, or even order dependent. Lastly, repeatedusage of the phrase “in one embodiment” does not necessarily refer tothe same embodiment, although it may.

[0066] Whereas many alterations and modifications of the presentinvention will be comprehended by a person skilled in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. Therefore, references todetails of particular embodiments are not intended to limit the scope ofthe claims.

What is claimed is:
 1. A method comprising: configuring a circuitemulation service (CES) over an internet protocol (IP) network based onproperties of the IP network, the CES being configured from a localinterworking function to a remote interworking function; encapsulatingdata received at a constant bit rate at the local interworking functioninto a plurality of IP packets configured according to the CES; andtransporting the IP packets from the local interworking function to theremote interworking function according to the CES.
 2. The method ofclaim 1 wherein the properties of the IP network comprise at least oneof a maximum delay variation, a bit error rate, out-of-order IP packetdelivery, and an unpredictable packet loss rate.
 3. The method of claim1 wherein configuring the CES comprises establishing a tunnel to carrythe plurality of IP packets between the local and remote interworkingfunctions.
 4. The method of claim 3 wherein the tunnel comprises a layer2 tunneling protocol (L2TP) tunnel and L2TP tunnel session within theL2TP tunnel.
 5. The method of claim 3 wherein the tunnel comprises amulti-protocol label switching (MPLS) tunnel.
 6. The method of claim 1wherein configuring the CES comprises: exchanging a plurality of CEScontrol protocol (CESCP) information between the local interworkingfunction and the remote interworking function.
 7. The method of claim 6wherein the plurality CESCP information comprises at least one of acircuit identification and an internet protocol address for the localand remote interworking functions, alarm indication signal options, idlecondition options, a clock option, a check sum option, a minimum and amaximum circuit size, a multiple circuits option, a maximum transitiondelay, a maximum delay variation, a compression option, and anencryption option.
 8. The method of claim 1 wherein encapsulating thedata comprises attaching a CES header to each IP packet.
 9. The methodof claim 8 wherein the CES header comprises a version number forcompatibility between the local interworking function and the remoteinterworking function.
 10. The method of claim 1 further comprising:buffering a plurality of IP packets received from the remoteinterworking function for at least as long as a maximum delay variation;and outputting payloads of the plurality of received IP packets at theconstant bit rate.
 11. The method of claim 10 wherein the maximum delayvariation comprises delay due to out-of-order IP packet delivery. 12.The method of claim 1 wherein each IP packet further comprises at leastone circuit, each circuit comprising at least one circuit header. 13.The method of claim 12 wherein the at least one circuit header comprisesat least one of a circuit identification, a flag field, a sequencenumber, a first octet padding value, a last octet padding value, and adata field.
 14. The method of claim 13 wherein the flag field comprisesat least one of a compression flag, an idle flag, an alarm indicationsignal flag, and a clocking information flag.
 15. The method of claim 14wherein the clocking information flag comprises a synchronous residualtime stamp (SRTS) value.
 16. The method of claim 13 wherein the sequencenumber indicates a starting position of a first bit of data in thecorresponding circuit with respect to a reference point in acorresponding bit stream.
 17. An article of manufacture comprising: amachine readable storage medium having stored thereon a pluralitymachine executable instructions; and said instructions, when executed,to implement a method comprising configuring a circuit emulation service(CES) over an internet protocol (IP) network based on properties of theIP network, the CES being configured from a local interworking functionto a remote interworking function; encapsulating data received at aconstant bit rate at the local interworking function into a plurality ofIP packets configured according to the CES; and transporting the IPpackets from the local interworking function to the remote interworkingfunction according to the CES.
 18. An apparatus comprising: firstcircuitry to configure a circuit emulation service (CES) over aninternet protocol (IP) network based on properties of the IP network,the CES being configured from a local interworking function to a remoteinterworking function; second circuitry to encapsulate data received ata constant bit rate at the local interworking function into a pluralityof IP packets configured according to the CES; and third circuitry totransport the IP packets from the local interworking function to theremote interworking function according to the CES.
 19. A methodcomprising: configuring a circuit emulation service (CES) over aninternet protocol (IP) network based on properties of the IP network,the CES being configured between a first interworking function to asecond interworking function; encapsulating data received at a constantbit rate at the first interworking function into a first plurality of IPpackets configured according to the CES; encapsulating data received atthe constant bit rate at the second interworking function into a secondplurality of IP packets configured according to the CES; transportingthe first plurality of IP packets from the first interworking functionto the second interworking function according to the CES; transportingthe second plurality of IP packets from the second interworking functionto the first interworking function according to the CES; buffering thesecond plurality of IP packets at the first interworking function for atleast as long as a maximum delay variation, said maximum delay variationcomprising delay due to out-of-order IP packet delivery; outputtingpayloads of the second plurality of IP packets at the constant bit rate;buffering the first plurality of IP packets at the second interworkingfunction for at least as long as the maximum delay variation; andoutputting payloads of the first plurality of IP packets at the constantbit rate;